AFTERTREATMENT SYSTEM WITH LEAN NOx TRAP FILTER

ABSTRACT

An aftertreatment system includes a first pipe section in fluid communication with an exhaust manifold on an internal combustion engine. A first aftertreatment device includes a housing and a porous substrate having substrate walls defining a plurality of flow channels including first channels obstructed at a first end of the substrate and second channels obstructed at a second end of the substrate opposite the first end. The first and second channels are interleaved and internal pore surfaces in the porous substrate form a plurality of internal pores. A passive NOx adsorption catalyst is deposited on the substrate walls and internal pore surfaces such that the mean porosity of the porous substrate is not greater than a particulate matter secondary grain size. A second aftertreatment device having an inlet is in fluid communication with the outlet of the first aftertreatment device.

TECHNICAL FIELD

The present disclosure generally relates to an aftertreatment system for exhaust gases from an internal combustion engine, and more particularly to an aftertreatment architecture having a lean NOx trap filter in combination with a selective catalyst reduction device.

BACKGROUND

Generally, vehicles, such as motor vehicles, are powered by a propulsion system. Certain motor vehicles employ an internal combustion engine, such as a Diesel engine, as a propulsion system, which provides power that is transferred to a transmission and used to drive the motor vehicle. To meet the recent, more stringent emissions regulations, an aftertreatment system having one or more after treatment devices may be employed to remove combustion byproducts, such as diesel particulate matter, carbon monoxide, nitrogen oxides (NOx), sulfur oxides (SOx), unburned hydrocarbons, and the like, from an exhaust stream prior to the exhaust stream being discharged from the internal combustion engine.

Conventional aftertreatment devices have particular working temperature ranges that must be reached to provide adequate conversion efficiencies. For example, a selective catalytic reduction (SCR) device may not reach adequate conversion efficiency until it attains a working temperature in the range of 200−300° C. In these situations, the aftertreatment system will not provide adequate conversion efficiencies at lower temperature ranges (e.g. below 200° C.) during engine start-up conditions or extremely low ambient operating conditions. An additional aftertreatment device such as a lean NOx trap (LNT) device may be included to extend the temperature range of the aftertreatment system for removing the combustion byproducts in lower temperature ranges. However, the LNT device may not be as efficient in removing the combustion byproducts as the SCR system in the higher working temperature range and another device for removing particulate matter.

Accordingly, it is desirable to provide a system and method of aftertreatment for an exhaust stream in one or more aftertreatment devices over a relatively wide working temperature range. The use of staged aftertreatment device would provide for efficient removal of combustion byproducts over a range of operating temperatures. Furthermore, other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.

SUMMARY

In accordance with the present disclosure, an exhaust gas aftertreatment device for exhaust gases from an internal combustion engine is provided. The aftertreatment device includes a housing having an inlet and an outlet. A porous substrate is disposed in the housing and includes substrate walls defining a plurality of flow channels including first channels obstructed at a first end of the substrate and second channels obstructed at a second end of the substrate opposite the first end. The first and second channels are interleaved and internal pore surfaces in the porous substrate form a plurality of internal pores that define tortuous passageways between the substrate walls. A passive NOx adsorption catalyst is deposited on the substrate walls and internal pore surfaces such that the mean porosity of the porous substrate is not greater than a particulate matter secondary grain size. In accordance with an additional embodiment, the mean porosity of the substrate is not less than 10 μm and not greater than 20 μm for adequately filtering particulate matter while limiting the pressure drop across the device.

In accordance with an additional embodiment, the porous substrate is uniformly coated with the catalyst such that the concentration of the catalyst on the substrate in the exhaust gas flow direction remains substantially constant over the length of the substrate. In accordance with an alternate embodiment, the porous substrate is zone coated with the catalyst such that the concentration of the catalyst varies over the length of the substrate to define distinct zones based on the catalyst concentration in each region of the substrate.

In accordance with an additional embodiment, the exhaust gas aftertreatment device further includes a Diesel oxidation catalyst section disposed in the housing between the inlet and the porous substrate.

In accordance with an additional embodiment, the exhaust gas aftertreatment device further includes a fuel injector configured to inject a hydrocarbon fuel into the exhaust gas stream downstream of the internal combustion engine and upstream of the porous substrate.

In accordance with the present disclosure, an aftertreatment system is disclosed for exhaust gas from an internal combustion engine having an exhaust manifold. The aftertreatment system includes a first pipe section configured to be in fluid communication with an exhaust manifold of the internal combustion engine. A first aftertreatment device includes a housing having an inlet and an outlet. A porous substrate is disposed in the housing and has substrate walls defining a plurality of flow channels including first channels obstructed at a first end of the substrate and second channels obstructed at a second end of the substrate opposite the first end. The first and second channels are interleaved and internal pore surfaces in the porous substrate form a plurality of internal pores that define tortuous passageways between the substrate walls. A passive NOx adsorption catalyst is deposited on the substrate walls and internal pore surfaces such that the mean porosity of the porous substrate is not greater than a particulate matter secondary grain size. A second aftertreatment device includes an inlet in fluid communication with the outlet of the first aftertreatment device. In accordance with an additional embodiment, the porous substrate in the first aftertreatment device has a mean porosity not less than 10 μm and not greater than 20 μm for adequately filtering particulate matter while limiting the pressure drop across the device.

In accordance with an additional embodiment, the porous substrate in the first aftertreatment device is uniformly coated with the catalyst such that the concentration of the catalyst on the substrate in the exhaust gas flow direction remains substantially constant over the length of the substrate. In accordance with an alternate embodiment, the porous substrate in the first aftertreatment device is zone coated with the catalyst such that the concentration of the catalyst varies over the length of the substrate to define distinct zones based on the catalyst concentration in each region of the substrate.

In accordance with an additional embodiment, the aftertreatment system further includes a Diesel oxidation catalyst section disposed in the housing between the inlet and the porous substrate.

In accordance with an additional embodiment, the aftertreatment system further includes a fuel injector configured to inject a hydrocarbon fuel into the aftertreatment system downstream of the exhaust manifold and upstream of the first aftertreatment device.

In accordance with an additional embodiment, the second aftertreatment device includes a selective catalytic reduction (SCR) unit downstream of the first aftertreatment device. In accordance with an additional embodiment, the aftertreatment system further includes a fluid injector configured to inject a diesel exhaust fluid into the aftertreatment system downstream of the first aftertreatment device and upstream of the SCR unit.

In accordance with an additional embodiment, the first aftertreatment device has a NOx conversion efficiency greater than 40% in a first temperature range between about 100° C. and 300° C. and the second aftertreatment device has a NOx conversion efficiency greater that 55% in a second temperature range between about 200° C. and 450° C.

In accordance with an additional embodiment, the aftertreatment system further includes a second pipe section having a first end in fluid communication with the outlet of the first aftertreatment device and a second end in fluid communication with the SCR unit such that second pipe section separates the first and second aftertreatment devices. In accordance with an additional embodiment, the aftertreatment system further includes a low-pressure exhaust gas recirculation circuit in fluid communication with the second pipe section.

DESCRIPTION OF THE DRAWINGS

The exemplary embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements.

FIG. 1 schematically shows an automotive system according to an embodiment of the present disclosure;

FIG. 2 is the section A-A of an internal combustion engine belonging to the automotive system of FIG. 1;

FIG. 3 shows an aftertreatment system having a first aftertreatment device in the form of a lean NOx trap (LNT) filter upstream of a second aftertreatment device in the form of a selective catalytic reduction (SCR) unit;

FIG. 4 shows an aftertreatment system having a first aftertreatment device including a Diesel oxidation catalyst (DOC) and an LNT filter upstream of a second aftertreatment device in the form of an SRC unit;

FIG. 5 is a schematic representation showing a cross-section of a LNT filter;

FIG. 6A is a detail of the LNT filter shown in FIG. 5 indicating the exhaust gas flow through the LNT filter; and

FIG. 6B is a detail at 6B of FIG. 6A indicating the exhaust gas flow through the porous substrate.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the invention disclosed herein or the application and uses of the invention disclosed herein. Furthermore, there is no intention to be bound by any principle or theory, whether expressed or implied, presented in the preceding technical field, background, summary or the following detailed description, unless explicitly recited as claimed subject matter.

Some embodiments may include an automotive system 10, as shown in FIGS. 1 and 2, that includes an internal combustion engine (ICE) 12 having an engine block 14 defining at least one cylinder 16 having a piston 18 coupled to rotate a crankshaft 20. A cylinder head 22 cooperates with the piston 18 to define a combustion chamber 24. A fuel and air mixture may be injected in the combustion chamber 24 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 18. The fuel is provided at high pressure to the fuel injector 26 from a fuel rail 28 in fluid communication with a high pressure fuel pump 30 that increase the pressure of the fuel received from a fuel source 32. The air is provided through at least one intake port 34. Each of the cylinders 16 has at least two valves 36, actuated by a camshaft 38 rotating in time with the crankshaft 20. The valves 36 selectively allow air through the intake port 34 into the combustion chamber 24 and alternately allow exhaust gases to exit through an exhaust port 40. In some examples, a cam phaser 42 may selectively vary the timing between the camshaft 38 and the crankshaft 20.

The air may be distributed to the air intake port(s) 34 through an intake manifold 44. An air intake duct 46 may provide air from the ambient environment to the intake manifold 44. In other embodiments, a throttle body 48 may be provided to regulate the flow of air into the manifold 44. In still other embodiments, a forced air system such as a turbocharger 50, having a compressor 52 rotationally coupled to a turbine 54, may be provided. Rotation of the compressor 52 increases the pressure and temperature of the air in the duct 46 and manifold 44. An intercooler 56 disposed in the duct 46 may reduce the temperature of the air. The turbine 54 rotates by receiving exhaust gases from an exhaust manifold 58 that directs exhaust gases from the exhaust ports 40 and through a series of vanes prior to expansion through the turbine 54. This example shows a variable geometry turbine (VGT) with a VGT actuator 60 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 54. In other embodiments, the turbocharger 50 may be fixed geometry and/or include a waste gate.

The exhaust gases exit the turbine 54 and are directed into an aftertreatment system 62. The aftertreatment system 62 may include an exhaust pipe 64 having one or more exhaust aftertreatment devices 66.1, 66.2. The aftertreatment devices 66.1, 66.2 (collectively 66) may be any device configured to change the composition of the exhaust gases. Additional details concerning preferred aftertreatment devices 66 are provided below. As illustrated, the internal combustion engine 12 includes a high-pressure short-route exhaust gas recirculation (HP-EGR) circuit 68 coupled between the exhaust manifold 58 and the intake manifold 44. The HP-EGR circuit 68 may include an EGR cooler 70 to reduce the temperature of the exhaust gases in the EGR circuit 68. An HP-EGR valve 72 regulates a flow of high-pressure exhaust gases in the HP-EGR circuit 68. The internal combustion engine 12 also includes a low-pressure, long-route exhaust gas recirculation (LP-EGR) circuit 74 coupled to the exhaust pipe 64 downstream of the turbine 54 and recirculates exhaust gasses into the air intake duct 46 upstream of the compressor 52. An LP-EGR valve 76 regulates a flow of low-pressure exhaust gases in the LP-EGR circuit 74.

The automotive system 10 may further include an electronic control unit (ECU) 78 in communication with one or more sensors and/or devices associated with the ICE 12. The ECU 78 may include a digital central processing unit (CPU) in communication with a memory system, or data carrier 80, and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices. The program may embody the methods disclosed herein, allowing the CPU to carry out the steps of such methods and control the ICE 12. Instead of an ECU 78, the automotive system 100 may have a different type of processor to provide the electronic logic, e.g. an embedded controller, an onboard computer, or any processing module that might be deployed in the vehicle.

The program stored in the memory system is transmitted from outside via a cable or in a wireless fashion. Outside the automotive system 10 it is normally visible as a computer program product, which is also called computer readable medium or machine readable medium in the art, and which should be understood to be a computer program code residing on a carrier, said carrier being transitory or non-transitory in nature with the consequence that the computer program product can be regarded to be transitory or non-transitory in nature.

An example of a transitory computer program product is a signal, e.g. an electromagnetic signal such as an optical signal, which is a transitory carrier for the computer program code. Carrying such computer program code can be achieved by modulating the signal by a conventional modulation technique such as QPSK for digital data, such that binary data representing said computer program code is impressed on the transitory electromagnetic signal. Such signals are e.g. made use of when transmitting computer program code in a wireless fashion via a Wi-Fi connection to a laptop.

In case of a non-transitory computer program product the computer program code is embodied in a tangible storage medium. The storage medium is then the non-transitory carrier mentioned above, such that the computer program code is permanently or non-permanently stored in a retrievable way in or on this storage medium. The storage medium can be of conventional type known in computer technology such as a flash memory, an Asic, a CD or the like.

The ECU 78 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 12. The sensors include, but are not limited to, a mass airflow and temperature sensor 82, a manifold pressure and temperature sensor 84, a combustion pressure sensor 86, coolant and oil temperature and level sensors 88, a fuel rail pressure sensor 90, a cam position sensor 92, a crank position sensor 94, a differential pressure sensor 96, an exhaust gas temperature sensors 98, an EGR temperature sensor 100, and an accelerator pedal position sensor 102. Furthermore, the ECU 78 may generate output signals to various control devices that are arranged to control the operation of the ICE 12, including, but not limited to, combustion fuel injectors 26, throttle body 48, EGR valves 72, 76 the VGT actuator 60, cam phaser 42 and aftertreatment fuel injector 104. Note, dashed lines are used to indicate communication between the ECU 78 and the various sensors and devices, but some are omitted for clarity.

With reference now to FIG. 3, an aftertreatment system 300 in accordance with the present disclosure will be further described. It should be appreciated that aftertreatment system 300 further details the components and configuration of the architecture for the aftertreatment system 62 shown in FIG. 1. The aftertreatment system 300 includes a first pipe section 302 having a first end in fluid communication the exhaust manifold 58 (shown in FIG. 1) and a second end in fluid communication with an inlet 304 of a first aftertreatment device 306. In the embodiment shown in FIG. 3, the first aftertreatment device is a lean NOx trap (LNT) filter 306. The LNT filter 306 is a catalyst system developed to decrease both particulate matter (PM) and nitrogen oxides (NOx) in a single unit. Additional details of the LNT filter are set forth below. Several sensors 310, 312, 314 are positioned at the inlet 304 and several sensors 316, 318, 320 are positioned at the outlet 322 of the first aftertreatment device 306 and provide sensor signals to the ECU 78 for controlling the aftertreatment system 300. These sensors include oxygen/NOx sensors (aka lambda sensors) 310, 320, exhaust gas temperature sensors 312, 318 and differential pressure sensors 314, 316.

A first AT (aftertreatment) injector 308 is configured to inject hydrocarbon (HC) fuel into the exhaust gas stream downstream of the exhaust manifold and independent from the fuel injectors 26 of the internal combustion engine 12. As illustrated herein, the first AT injection 308 is located in the first pipe section 302 downstream of the turbocharger 50. However, one skilled in the art should understand that the first AT fuel injector 308 may be in the exhaust system upstream of the turbocharger 50. The ECU 78 is in communication with the first AT injector 308 for precisely controlling HC injections into the aftertreatment system 300. In general, the AT fuel injector 308 has similar components and functions to the combustion fuel injectors 26 with the exception that it is intended to operate at a lower working pressure. Implementation of a dedicated AT fuel injector, instead of a post injection strategy with fuel injectors 26, provides several distinct advantages for reducing particulate matter and NOx production. Controlling the aftertreatment HC injection independent of combustion injections removes any practical limitation of operational range otherwise imposed with post-injection rich strategies. As such HC emissions can be controlled by increasing the rich-spike frequency and the number of injections independent of combustions constraint. Moreover, the AT fuel injector may be used in combinations with multiple after injections to reduce the possibility of oil dilution.

The aftertreatment system 300 includes a second pipe section 324 having a first end in fluid communication with an outlet 322 of the lean NOx trap filter 306 and a second end in fluid communication with an inlet 326 of a second aftertreatment device 328. In the embodiment shown in FIG. 3, the second aftertreatment device 328 is a selective catalytic reduction (SCR) unit. A second AT injector 330 is configured to inject diesel exhaust fluid or urea (DEF) into the exhaust gas stream downstream of the first aftertreatment device 306. The ECU 78 is in communication with the second AT injector 330 for precisely controlling DEF injections into the aftertreatment system 300. An oxygen/NOx sensor (aka lambda sensor) 332 is positioned at the outlet 334 of the second aftertreatment device 328 and provides sensor signals to the ECU 78 for controlling the aftertreatment system 300. The aftertreatment system 300 includes a third pipe section 336 having a first end in fluid communication with the outlet 334 of the second aftertreatment device 328. The LP-EGR circuit 74 (shown in FIG. 1) is in fluid communication with the second pipe section 324 for recirculating a portion of the exhaust gas passing therethrough to the inlet manifold 44 as previously indicated.

With reference now to FIG. 4, an aftertreatment system 400 in accordance with the present disclosure will be further described. It should be appreciated that aftertreatment system 400 further details the components and configuration of the architecture for the aftertreatment system 62 shown in FIG. 1. The aftertreatment system 400 includes a first pipe section 402 having a first end in fluid communication the exhaust manifold 58 (shown in FIG. 1) and a second end in fluid communication with an inlet 404 of a first aftertreatment device 406. In the embodiment shown in FIG. 4, the first aftertreatment device 406 is multi-function aftertreatment device having a diesel oxidation catalyst (DOC) section 406.1 upstream of a lean NOx trap (LNT) filter 406.2. Several sensors 410, 412, 414 are positioned at the inlet 404 and several sensors 416, 418, 420 are positioned at the outlet 422 of the first aftertreatment device 406 and provide sensor signals to the ECU 78 for controlling the aftertreatment system 400. These sensors include oxygen/NOx sensors (aka lambda sensors) 410, 420, exhaust gas temperature sensors 412, 418 and differential pressure sensors 414, 416.

A first AT (aftertreatment) injector 408 is configured to inject hydrocarbon (HC) fuel into the exhaust gas stream downstream of the exhaust manifold and independent from the fuel injectors 26 of the internal combustion engine 12. As illustrated herein, the first AT injection 408 is located in the first pipe section 402 downstream of the turbocharger 50. However, one skilled in the art should understand that the first AT injector 408 may be located in the exhaust system upstream of the turbocharger 50. The ECU 78 is in communication with the first AT injector 408 for precisely controlling HC injections into the aftertreatment system 400.

The aftertreatment system 400 includes a second pipe section 424 having a first end in fluid communication with an outlet 422 of the first aftertreatment device 406 and a second end in fluid communication with an inlet 426 of a second aftertreatment device 428. In the embodiment shown in FIG. 4, the second aftertreatment device 428 is a selective catalytic reduction (SCR) unit. A second AT injector 430 is configured to inject diesel exhaust fluid or urea (DEF) into the exhaust gas stream downstream of the first aftertreatment device 406. The ECU 78 is in communication with the second AT injector 430 for precisely controlling DEF injections into the aftertreatment system 400. An oxygen/NOx sensor (aka lambda sensor) 432 is positioned at the outlet 434 of the second aftertreatment device 428 and provides sensor signals to the ECU 78 for controlling the aftertreatment system 400. The aftertreatment system 400 includes a third pipe section 436 having a first end in fluid communication with the outlet 434 of the second aftertreatment device 428. The LP-EGR circuit 74 (shown in FIG. 1) is in fluid communication with the second pipe section 424 for recirculating a portion of the exhaust gas passing therethrough to the inlet manifold 44 as previously indicated.

The SCR unit 328 used in the aftertreatment system 300 and the diesel oxidation catalyst section 406.1 and the SCR unit 428 used in the aftertreatment system 400 described above are adapted using conventional technology for selective catalytic reduction and oxidation of compounds with a reducing character such as hydrocarbons and sulfate particulates. Thus, further discussion of the substrates, catalytic treatments and regeneration processes are not further discussed herein.

With reference to FIG. 5, a lean NOx trap (LNT) filter 500, as represented by 306 in aftertreatment system 300 and 406.2 in the aftertreatment system 400, includes a housing 502 having an inlet 504 and an outlet 506. The housing encloses a porous substrate 508 having inlet flow channels 510 i interleaved with outlet flow channels 510 o bounded by the porous substrate 508. In this regard, an inlet flow channel 510 i is open at an end 512 adjacent to the inlet 504 and blocked by a plug 514 at an end 516 adjacent the outlet 506. Conversely, an outlet flow channel 510 o is blocked by a plug 518 at the end 512 adjacent the inlet 504 and open at the end 516 adjacent the outlet 506. Plugs 514, 518 are significantly less porous than the porous substrate 508 to ensure that exhaust gas is not permitted to flow therethrough.

As shown in FIGS. 5 and 6A, exhaust gas EG flowing through the LNT filter 500 enters an inlet flow channel 510 i and is force through the porous substrate 508 and into an outlet flow channel 510 o. Exhaust gas may flow through more than one inlet flow channel and/or one exhaust flow channel depending on the differential pressures therein. With reference to FIG. 6B, the porous substrate 508 forms substrate walls 520 and internal pore surfaces 522 having a plurality of internal pores 524 that define tortuous passageways between the substrate walls 520. The porous substrate 508 is coated a passive NOx adsorption catalyst 526 such that the substrate walls 520 and internal pore surfaces 522 have an exposed layer of catalyst. Conventional acid-based washcoat chemistry for a passive NOx adsorption catalyst (e.g., zeolites-based catalysts and/or alkali/alkaline oxide constituents) may be used as catalyst 526 for adsorbing NOx under lower temperature conditions such as during vehicle cold starts and releasing NOx when the temperature of the exhaust gas increases without requiring a rich regeneration cycle. Other passive or partially active NOx adsorption catalysts which are effective to control cold start/low temperature NOx emissions may be implemented as the catalyst 526 in the present disclosure.

In one embodiment, the concentration of the catalyst 526 on the substrate 508 in the exhaust gas flow direction remains substantially constant over the length of the substrate 508 such that it is generally uniformly coated. In an alternate embodiment, the concentration of catalyst 526 on the substrate 508 in the exhaust gas flow direction may be varied over the length of the substrate 508 such distinct zones are defined based on the catalyst concentration in each region of the substrate 508. In other words, the substrate is zone-coated to promote Diesel particulate filter regeneration in this alternate embodiment.

The material of the porous substrate 508 is selected to filter particulate matter in the exhaust gases having an aerodynamic diameter in the range of about 10 to 20 micrometers (μm), which generally corresponds to the secondary grain size of the particulate matter. Particulate matter in the exhaust gases having an aerodynamic diameter larger than about 20 μm are filtered at the interface of the substrate wall 520, or in other words are trapped in the inlet flow channels 510 i. Particulate matter having an aerodynamic diameter smaller than about 10 μm pass through the internal pores 524 of the substrate 508. Deposition of the catalyst 526 on the internal pore surface 522 should be taken into account when selecting the material for the porous substrate to achieve the above-stated filtering function. In this regard, the mean porosity of the coated substrate is not greater than a particulate matter secondary grain size.

With reference now to FIGS. 6A and 6B in the context of FIGS. 3 and 4, exhaust gas EG enters the LNT filter 500 at the inlet end 512 and is directed into inlet flow channels 510 i (one being shown). A hydrocarbon fuel may be injected into the exhaust gas EG with the first AT injector 308, 408 based on the chemical composition of the exhaust gas EG and the desired stoichiometry for the first aftertreatment device 306, 406 to promote both particulate matter and NOx reduction. By using a dedicated injector, a higher NOx conversion efficiency can be reached with no potential limitation otherwise encountered as compared to conventional post-injection rich strategies. Likewise, hydrocarbon emissions can be control by increasing the rich-spike frequency and the number of injections with a dedicated injector, independent of fuel injections for combustion. Furthermore, the use of a dedicated injector in combination with multiple after injections may reduce oil dilution experienced with some conventional post-injection rich strategies.

Course particulate matter PM_(C) (>20 μm) in the exhaust gas EG is blocked at the substrate wall 520. Finer particulate matter PM_(F) (10-20 μm) in the exhaust gas is trapped in the internal pores 524 of the porous substrate 508. In addition, the catalyst 526 deposited on the substrate walls 520 and the internal pore surfaces 522 adsorbs NOx in the exhaust gas under cold start/low temperature operating conditions. A treated exhaust gas, from which particulate matter has been filtered and a reduction in the NOx concentration in the exhaust gas EG has achieved under cold start/low temperature operating conditions is discharged through outlet 506 downstream. At conventional engine operating temperatures, a thermal reaction reverses the NOx adsorption on the catalyst 526. As such, NOx trapped in the first aftertreatment device 306, 406 is passed through the second aftertreatment device 328, 428. Since the aftertreatment system is at conventional engine operating temperatures, the SCR unit 328, 428 is effective in the reduction and oxidation of NOx and other combustion byproducts in the treated exhaust gas TEG.

By employing an LNT filter in combination with an SCR unit, the aftertreatment system 300, 400 is effective over a wide temperature range from about 100° C. to above 400° C. As presently preferred, the first aftertreatment device 306, 406 is configured to have a NOx conversion efficiency greater than 40% in a first temperature range between about 100° C. and 300° C. and the second aftertreatment device 328, 428 is configured to have a NOx conversion efficiency greater that 55% in a second temperature range between about 200° C. and 450° C. The LNT filter 306. 406.2 can simultaneously reduce particulate matter and NOx in a single unit with a smaller catalyst volume than a system employing separate lean NOx trap and Diesel particulate filter. The LNT filter 306, 406.2 also advantageously compares to other devices in that the catalyst employed therein does not conflict with platinum group metals (PGMs) which would otherwise poison the catalyst used in a selective catalyst reduction filter (SCRF) unit. Moreover, the configuration of an LNT filter 306, 406.2 separate from the SCR unit 328, 428 provides protection from damage to the DEF injector assembly 330, 430 resulting from over-temperature conditions.

While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the disclosure as set forth in the appended claims and the legal equivalents thereof. 

1. An exhaust gas aftertreatment device for exhaust gases from an internal combustion engine comprising: a housing having an inlet and an outlet; a porous substrate having substrate walls defining a plurality of flow channels formed therein including first channels obstructed at a first end of the substrate and second channels obstructed at a second end of the substrate opposite the first end, wherein the first and second channels are interleaved and internal pore surfaces in the porous substrate form a plurality of internal pores that define tortuous passageways between the substrate walls; and a passive NOx adsorption catalyst deposited on the substrate walls and internal pore surfaces such that the mean porosity of the porous substrate is not greater than a particulate matter secondary grain size.
 2. The exhaust gas aftertreatment device according to claim 1, wherein the mean porosity of the substrate is not less than 10 μm and not greater than 20 μm.
 3. The exhaust gas aftertreatment device according to claim 1, wherein the porous substrate is uniformly coated with the catalyst such that the concentration of the catalyst on the substrate in the exhaust gas flow direction remains substantially constant over the length of the substrate.
 4. The exhaust gas aftertreatment device according to claim 1, the porous substrate is zoned coated with the catalyst such that the concentration of the catalyst varies over the length of the substrate to define distinct zones based on the catalyst concentration in a given region of the substrate.
 5. The exhaust gas aftertreatment device according to claim 1, further comprising a Diesel oxidation catalyst section disposed in the housing between the inlet and the porous substrate.
 6. The exhaust gas aftertreatment device according to claim 1, further comprising a fuel injector configured to inject a hydrocarbon fuel into the exhaust gas stream downstream of the internal combustion engine and upstream of the porous substrate.
 7. An aftertreatment system for exhaust gas from an internal combustion engine having an exhaust manifold, the aftertreatment system comprising: a first pipe section configured to be in fluid communication with the exhaust manifold; a first aftertreatment device including a housing having an inlet and an outlet, a porous substrate having substrate walls defining a plurality of flow channels formed therein including first channels obstructed at a first end of the substrate and second channels obstructed at a second end of the substrate opposite the first end, wherein the first and second channels are interleaved and internal pore surfaces in the porous substrate form a plurality of internal pores that define tortuous passageways between the substrate walls, and a passive NOx adsorption catalyst deposited on the substrate walls and internal pore surfaces such that the mean porosity of the porous substrate is not greater than a particulate matter secondary grain size; a second aftertreatment device having an inlet in fluid communication with the outlet of the first aftertreatment device.
 8. The aftertreatment system according to claim 7, wherein the porous substrate in the first aftertreatment device has a mean porosity not less than 10 μm and not greater than 20 μm.
 9. The aftertreatment system according to claim 7, wherein the porous substrate in the first aftertreatment device is uniformly coated with the catalyst such that the concentration of the catalyst on the substrate in the exhaust gas flow direction remains substantially constant over the length of the substrate.
 10. The aftertreatment system according to claim 7, wherein the porous substrate in the first aftertreatment device is zoned coated with the catalyst such that the concentration of the catalyst varies over the length of the substrate to define distinct zones based on the catalyst concentration in a given region of the substrate.
 11. The aftertreatment system according to claim 7, further comprising a Diesel oxidation catalyst section disposed in the housing between the inlet and the porous substrate.
 12. The aftertreatment system according to claim 7 further comprising a fuel injector configured to inject a hydrocarbon fuel into the aftertreatment system downstream of the exhaust manifold and upstream of the first aftertreatment device.
 13. The aftertreatment system according to claim 7, wherein the second aftertreatment device comprises a selective catalytic reduction (SCR) unit.
 14. The aftertreatment system according to claim 13, further comprising a fluid injector configured to inject a diesel exhaust fluid into the aftertreatment system downstream of the first aftertreatment device and upstream of the SCR unit.
 15. The aftertreatment system according to claim 7 wherein the first aftertreatment device has a NOx conversion efficiency greater than 40% in a first temperature range between about 100° C. and 300° C. and the second aftertreatment device has a NOx conversion efficiency greater that 55% in a second temperature range between about 200° C. and 450° C.
 16. The aftertreatment system according to claim 7, further comprising a second pipe section having a first end in fluid communication with the outlet of the first aftertreatment device and a second end in fluid communication with the second aftertreatment device such that second pipe section separates the first and second aftertreatment devices.
 17. The aftertreatment system according to claim 16, further comprising a low-pressure exhaust gas recirculation circuit in fluid communication with the second pipe section. 